JP6550602B2 - Optical microphone - Google Patents

Description

  The present invention relates to an optical microphone capable of reducing distortion of an audio output signal.

  There is known an optical microphone that irradiates light to a diaphragm that vibrates upon receiving a sound wave, detects the displacement of the diaphragm by receiving reflected light from the diaphragm with a light receiving element, and outputs this detection signal as an audio signal. ing. The optical microphone described in Patent Document 1 is an example.

  The optical microphone described in Patent Document 1 receives a diaphragm that vibrates in response to sound waves, a light-projection-side light guide that emits light from the light source toward the diaphragm, and reflected light from the diaphragm. And a light receiving side light guide that leads to the light receiving element. The sensitivity of this optical microphone is determined by the amount of light that can be reflected by the diaphragm and incident on the light receiving side light guide. Therefore, in the above-described optical microphone, an elastic member is interposed between the light projecting side light guide and the light receiving side light guide, and the compression force applied to the elastic member from the light projecting side light guide and the light receiving side light guide is applied. The sensitivity can be adjusted by adjusting.

  According to the optical microphone as described in Patent Document 1, when the distance between the light exit surface of the light emitting side light guide and the light incident surface of the light receiving side light guide and the diaphragm increases, the light receiving side light guide is used. Increasing the amount of incident light increases the sensitivity. However, if the interval is larger than a certain level, the optical path from the light source to the light receiving element becomes longer, and the sensitivity is lowered. Therefore, the sensitivity adjustment of the optical microphone is performed in the range of the interval suitable for the sensitivity adjustment.

  According to the optical microphone, when the vibration plate vibrates upon receiving a sound wave, the distance between the light emitting side light guide and the light receiving side light guide and the vibration plate fluctuates. Therefore, the sound output level differs between the case of vibrating in the direction approaching the light emitting side light guide and the light receiving side light guide and the case of vibrating in the direction of getting away. That is, distortion occurs in the audio output signal, and an audio output signal faithful to the voice can not be obtained.

JP2015-156617A

  An object of the present invention is to provide an optical microphone capable of reducing distortion of an audio output signal.

The present invention
A diaphragm that vibrates in response to sound waves,
A projection-side light guide that emits light from a light source toward the diaphragm;
A light receiving side light guide that receives reflected light from the diaphragm and guides it to a light receiving element;
An optical microphone to which an audio signal is output from the light receiving element,
Two pairs of light guides composed of the light projecting side light guide and the light receiving side light guide arranged in parallel are disposed symmetrically across the diaphragm,
The most important feature is that the audio signals of the light receiving elements of the two pairs of light guides are synthesized and output.

  When the diaphragm receives a sound wave and the diaphragm moves away from one light guide pair, the diaphragm moves toward the other light guide pair. Therefore, the drop of the output signal from one light guide pair is compensated by the increase of the output signal from the other light guide pair, and an optical microphone with less distortion of the audio output signal can be obtained.

FIG. 1 is a longitudinal sectional view schematically showing an embodiment of an optical microphone according to the present invention. It is a perspective view which shows the external appearance of the said Example.

  Embodiments of an optical microphone according to the present invention will be described below with reference to the drawings.

  1 and 2, the optical microphone 1 has a diaphragm 2 called a membrane, two pairs of light guides 10 and 20, and housings 100 and 200. One light guide pair 10 is incorporated in the housing 100, and the other light guide pair 20 is incorporated in the housing 200. The diaphragm 2 is a circular member made of a thin film-like material, and its peripheral edge portion is fixed by applying appropriate tension to the lower surface of the holding ring 220 in FIG.

  The diaphragm 2 is mounted on the upper end surface of the housing 100 while being held by the holding ring 220. The lower end of the housing 200 is placed on the holding ring 220, and the holding ring 220 is sandwiched between the upper and lower housings 100 and 200 and fixed to each other. In this manner, one ends of the two housings 100 and 200 are fixed to each other with the peripheral portion of the diaphragm 2 interposed therebetween, with the holding ring 220 interposed. When receiving the sound wave, the diaphragm 2 vibrates on the inner peripheral side of the holding ring 220.

  In the housing 100, a light source 12 and a light receiving element 13 which are light emitting elements such as LEDs are incorporated. Further, the light guide pair 10 including the light-projecting side light guide 14 and the light-receiving side light guide 15 is also incorporated in the housing 100 in parallel in the length direction. The light projecting side light guide 14 is disposed so as to guide the light from the light source 12 upward in FIG. The light guided by the light projecting side light guide 14 is emitted from the upper emission surface 143 toward the diaphragm 2. The lower surface of the diaphragm 2 is a reflecting surface.

  The light receiving side light guide 15 is disposed so as to guide light from the reflecting surface of the diaphragm 2 downward in FIG. Therefore, the lower surface of the diaphragm 2 reflects the light emitted from the light projecting side light guide 14 toward the light receiving side light guide 15. This reflected light is guided into the light receiving side light guide 15 from the incident surface 153 at the upper end of the light receiving side light guide 15. The reflected light is guided downward along the light receiving side light guide 15 and received by the light receiving element 13.

  In the present embodiment, the light projecting side light guide 14 and the light receiving side light guide 15 are arranged in parallel with each other in the length direction. A light shielding member 16 is interposed between the light projecting side light guide 14 and the light receiving side light guide 15.

  At the front end portion of the light projecting side light guide 14, a cut surface inclined to the side opposite to the light receiving side light guide 15 is formed. The formation of the cut surface limits the light emission surface 43. A light reflecting surface 141 is formed on the cut surface of the light projecting side light guide 14 by coating a reflecting film or the like.

  Also at the front end portion of the light receiving side light guide 15, a cut surface inclined to the side opposite to the light projecting side light guide 14 is formed. By forming the cut surface, the light incident surface 153 is limited. A light reflecting surface 151 is also formed on the cut surface of the light-receiving side light guide 15 by coating a reflecting film or the like. The light emitting side light guide 14 and the light receiving side light guide 15 are arranged back to back with the light shielding member 16 in between. On the back-to-back surfaces of the light projecting side light guide 14 and the light receiving side light guide 15, light reflecting films 142 and 152 are formed, respectively.

  As described above, the light emitting side light guide 14 has its light emitting surface 143 limited. The light emitting side light guide 14 is formed with an inclined reflecting surface 141 and a reflecting film 142. As a result, light from the light source 12 guided in the light projecting side light guide 14 is intensively emitted from the emission surface 143. Also by forming the reflective film 142, the light from the light source 12 is efficiently guided in the light projecting side light guide 14. In this way, light is intensively emitted from the emission surface 143.

  The concentrated outgoing light is reflected by the diaphragm 2. The reflected light enters the light receiving side light guide 15 from the incident surface 153 of the light receiving side light guide 15. The light entering the light receiving side light guide 15 is reflected by the reflecting surface 151 and the reflecting film 152. As a result, the light incident on the light receiving side light guide 15 is guided toward the light receiving surface of the light receiving element 13 and is efficiently received by the light receiving element 13. Thus, the light projecting side light guide 14 and the light receiving side light guide 15 efficiently guide the light from the light source 12 to the light receiving element 13.

  As indicated by the oblique arrow lines in FIG. 1, the emission range of the light emitted from the emission surface 143 of the light projection side light guide 14 gradually expands toward the diaphragm 2. Conversely, the incident range of the light reflected by the diaphragm 2 and incident on the incident surface 153 of the light receiving side light guide 15 is gradually narrowed toward the incident surface 153. In this embodiment, the range where the emission range and the incidence range overlap is the sensing unit 30. The sensitive part is an area where the diaphragm 2 detects sound waves. Therefore, if the sensitive part 30 is wide, the sensitivity of the microphone increases. When the intervals between the exit surface 143 and the entrance surface 153 and the diaphragm 2 are narrowed, the sensitive part 30 is narrowed and the sensitivity is lowered. This is because the amount of light reaching the light receiving portion, that is, the light receiving element 13 changes depending on the size of the sensing portion.

  1 and 2, the light guide pair 20 incorporated in the upper housing 200 is configured in the same manner as the light guide pair 10. Hereinafter, the light guide pair 20 will be described. However, since the configuration is the same as that of the light guide pair 10, only a schematic description will be given.

  The light guide pair 20 includes a light source 22 and a light receiving element 23, and includes a light projecting side light guide 24, a light receiving side light guide 25, and a light blocking member 26. These members are configured in the same manner as the corresponding members in the light guide pair 10. Further, the light projection side light guide 24 has a light reflection surface 241, a light emission surface 243, and a light reflection film 242, similarly to the light projection side light guide 14 of the light guide pair 10. Similar to the light receiving side light guide 15 of the light guide pair 10, the light receiving side light guide 25 has a light incident surface 253, a light reflecting surface 251, and a light reflecting film 252.

  A light guide pair 20 including a light projecting side light guide 24 and a light receiving side light guide 25 is also incorporated in the housing 200 in parallel in the length direction. The light projecting side light guide 24 is arranged so as to guide light from the light source 22 downward in FIG. The light guided by the light projecting side light guide 24 is emitted from the lower emission surface 243 toward the diaphragm 2. The upper surface of the diaphragm 2 is also a reflecting surface.

  In the optical microphone 1 according to the above embodiment, two pairs of light guides 10 and 20 including a light-projecting-side light guide and a light-receiving-side light guide arranged in parallel are disposed symmetrically with the diaphragm 2 in between. ing. The distance between the exit surface 243 and the entrance surface 253 of one light guide pair 20 and the diaphragm 2 is the distance between the exit surface 143 and the entrance surface 153 of the other light guide pair 10 and the diaphragm 2. Is the same.

  The upper housing 200 is provided with a plurality of window hole-like sound wave inlets 201. The sound wave introduced into the housing 200 from the sound wave introduction port 201 reaches the diaphragm 2 and vibrates the diaphragm 2. The periphery of the lower housing 100 is closed, and the housing 100 is not provided with a sonic inlet. Thus, the optical microphone according to the illustrated embodiment is omnidirectional. The lower housing 100 may also be provided with a sound wave introduction port to provide a directivity optical microphone different from the non-directivity.

  The audio signals output from the light receiving elements 13 and 23 of the two pairs of light guides 10 and 20 are combined to be an output signal of the optical microphone 1. Since this is substantially the same as preparing two optical microphones and combining the output signals of the respective optical microphones, the output signal level of the microphones is increased and the sensitivity is increased. In addition, secondary distortion of the audio output signal can be reduced. The reason is as follows.

  Assuming a conventional optical microphone as described in Patent Document 1 having a pair of light guides, the sensitivity is determined by the distance between the exit surface and the entrance surface of the light guide and the diaphragm, and the light source. Depends on the length of the optical path to the light receiving element. Therefore, in a situation where a large sound pressure is applied and the diaphragm is greatly displaced, the amount of light reflected by the diaphragm is greatly different between when the diaphragm moves forward and when it moves backward. As a result, since the amount of light received by the light receiving element is different, second-order distortion occurs in the audio output signal.

  According to the optical microphone 1 according to the illustrated embodiment, the second-order distortion is canceled by using the difference between the sound signals of the light receiving elements 13 and 23 of the two light guide pairs 10 and 20 as the sound output signal, Secondary distortion can be reduced. On the other hand, since the signals corresponding to the sound waves detected by the light receiving elements 13 and 23 have a complementary relationship, by taking the difference as described above, the output signal level is increased and the sensitivity is increased.

  In the optical microphone as in the present invention, it is desirable that the sound wave inlet 201 shown in the figure be blocked, for example, with a filter that passes the sound wave and blocks the external light so as not to be affected by the external light. For example, a metal vapor deposition film can be used as the filter. Alternatively, a film-like member having countless fine holes may be used.

  Alternatively, the light sources 12 and 22 are light emitting elements that emit light having a wavelength other than visible light, and the light receiving elements 13 and 23 are light receiving elements in a wavelength band that can detect light emitted from the light sources 12 and 22. This is effective in preventing the influence of external light.

  An optical microphone as in the present invention can perform electroacoustic conversion without being affected by an electric field or a magnetic field, whether in an electric field or in a magnetic field. For example, even in a medical examination site using an MRI phenomenon. Electroacoustic conversion with high accuracy is possible.

DESCRIPTION OF SYMBOLS 1 Optical microphone 2 Diaphragm 10 Light guide pair 12 Light source 13 Light receiving element 14 Light emission side light guide 15 Light reception side light guide 16 Light shielding member 20 Light guide pair 10 Light guide pair 22 Light source 23 Light receiving element 24 Light emission side light guide 25 Light reception Side light guide 26 Light shielding member 30 Sensed part 40 Sensed part 100 Housing 200 Housing 201 Sound wave introduction port

Claims (6)

A diaphragm that vibrates in response to sound waves,
A projection-side light guide that emits light from a light source toward the diaphragm;
A light receiving side light guide that receives reflected light from the diaphragm and guides it to a light receiving element;
An optical microphone to which an audio signal is output from the light receiving element,
Two pairs of light guides composed of the light projecting side light guide and the light receiving side light guide arranged in parallel are disposed symmetrically across the diaphragm,
An optical microphone for synthesizing and outputting audio signals of the light receiving elements of the two light guide pairs.   2. The pair of light guides and the other pair of light guides are assembled in separate housings, and one ends of the two housings are fixed to each other with a peripheral edge of the diaphragm interposed therebetween. Optical microphone.   The optical microphone according to claim 2, wherein at least one of the two housings has a sound wave introduction port.   The optical microphone according to claim 3, wherein the sound wave introduction port is closed by a filter that allows sound waves to pass therethrough and blocks outside light.   The optical microphone according to any one of claims 1 to 4, wherein the light source is a light emitting element for emitting light other than visible light, and the light receiving element detects light emitted from the light source.   The optical microphone according to any one of claims 1 to 5, wherein a light shielding member is interposed between the light emitting side light guide and the light receiving side light guide.

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